Unusual Cooke microscope objective

[old martParticipant @oldmart]

I bought a job lot of microscope objectives really cheap which were not in usable condition. This was to get hold of the bodies to convert some of my existing objectives to sprung because I have been destroying some slides lately. Amongst the collection were some which had been labeled as unfocussable, rather than the commoner delamination.

One is a Cooke X45 0.95 fluorite oil which is also marked LWD. I couldn’t see any trace of the common delamination which ruins most fluorites but couldn’t get it to focus with oil. This objective is rather short, about 33mm long, so I had to use a parfocal extender and was just giving up the tests when it snapped into focus. The working distance even with oil is about 1.5mm which needs a large drop of oil. It might get shoehorned into a Vickers body if I can reduce the body diameter by 0.35mm, or bore the Vickers out that much. It would probably be worth it as the image is very good.

 

 

[Michael GilliganParticipant @michaelgilligan61133]

Nice find … 1.5mm is certainly LWD

Sorry; don’t really understand your shoe-horning comments.

MichaelG.

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P.S. __ You might find this page of interest:

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep98/cts.html

[old martParticipant @oldmart]

The idea is to convert the Cooke to sprung nose.

As for the non focussing, the original owner and myself were trying to use the lens much too close to the slide and it was pure luck that I lowered the stage while still looking through the eyepieces. I have a cheap set of prepared slides which won’t work with higher magnification objectives, the cover slips are nearly 0.5mm thick.

[old mart]

On old mart Said:

The idea is to convert the Cooke to sprung nose.

[…]

Aah … that makes sense [if you feel the need to do so] … thanks for clarifying.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Listed at £11 16s in the late 1940s … this is a serious lens.

Apologies for the scan quality, it’s the best I have

 

MichaelG.

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[old martParticipant @oldmart]

I would normally avoid fluorite lenses as they are very prone to faults. They delaminate and it is impossible to clean the fluorite surface as it is soft. Fortunately, modern low dispersion glass formulations make fluorite obsolete. There was a time when some top end camera lenses also used fluorite elements, they tended to have short lifespans. The old Cooke is very rare not to have any optical deterioration that I can detect.

[Michael GilliganParticipant @michaelgilligan61133]

Now that you’ve got the feel for this objective … have you tried it without the ‘parfocal extender’ ?

MichaelG.

[old martParticipant @oldmart]

I have only tried it on my latest acquisition which I got by accident. An Olympus BHC. It had a start price of £120 and was being sold by a hospice charity near Swindon. They were reluctant to send it by post as it had failed PAT testing. I put in a higher bid expecting to get the ball rolling and turned out to be the only bidder. So I had a 122 mile drive to pick it up. A trinocular head, epi attachment, built in Kohler, a huge mechanical stage with 100mm movement in both axes. Also 5, 20, 40 and 100 parfocal MET plan objectives, all air gap in a five position turret. Two 10X wf eyepieces. And I already had an Olympus MET 10X which is parfocal with the others. It runs perfectly on LED lighting and I bought a biological mechanical stage which fits perfectly with a number of mods and interchanges with the original in seconds. The Biolam condensers fit, but the lighting system works very well without using one. The olympus 100 is 10mm longer than the 45 Cooke and the parfocal extender is needed to use it in its original form. If I fit it into a Vickers body with about 4mm spring movement, it can easily be that 10mm longer. I haven’t tried it in the Biolam R25 which will certainly have the greater movement.

[Michael GilliganParticipant @michaelgilligan61133]

Magnificent news of your almost unintended purchase !

I hadn’t realised where the Cooke lens was fitting into the grand scheme of things … I was merely hoping to see you get the best out of it ‘in isolation’

MichaelG.

[old martParticipant @oldmart]

In addition to that nice Cooke 45X, I also have a Cooke 95X NA 1.3 oil which also gives oustanding definition. The both are destined for fitting within the bodies of Vickers scrap objectives for making them sprung. I will be assembling a set of five to fit the Olympus BHC as follows.

Lomo 3.5 NA 0.1

Swift 10 NA 0.25

GS 25 NA not known

Cooke 45 NA 0.95 FL LWD oil

Cooke 95 NA 1.3 oil

I fancied getting a second nosepiece (turret) for the olympus but the prices of them was too high. Then a quintuple for the olympus BH2 came on ebay for a good price. They have a quick change wedge rather than the four screws for my older model. Close examination of the photographs comparing it to mine made me decide to take a chance and I got lucky, the wedge unscrews and then the only difference is the black plastic ring for turning the turret. Already having a full set of epi objectives on one turret and a full set of biological objectives on the other together with two lighting systems, both battery LED powered makes the Olympus the do everything microscope. I will have to think hard about my Lomo R25 and the Vickers M12.

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